palette

name	palette
description	Design BGR555 color palettes for the SNES menu ROM. Use when discussing colors, gradients, themes, or editing palette.a65 or HDMA gradient tables in const.a65.
argument-hint	[color-spec or theme-name]

SNES Palette Design Tool

Help design BGR555 color palettes for the sd2snes menu ROM.

BGR555 Conversion

Each color: 2 bytes little-endian. Bit layout: 0bbbbbgg_gggrrrrr (15-bit)

RGB to BGR555:

1. Scale 0-255 to 0-31: ch5 = round(ch8 / 255 * 31)
2. Pack: bgr555 = (blue5 << 10) | (green5 << 5) | red5
3. Split: low = bgr555 & 0xFF, high = (bgr555 >> 8) & 0xFF
4. Output: .byt $XX, $YY (low first)

Quick reference:

RGB Hex	BGR555 bytes	R,G,B (5-bit)
#000000	$00, $00	0, 0, 0
#FFFFFF	$FF, $7F	31, 31, 31
#FF0000	$1F, $00	31, 0, 0
#00FF00	$E0, $03	0, 31, 0
#0000FF	$00, $7C	0, 0, 31
#FF00FF	$1F, $7C	31, 0, 31
#FFFF00	$FF, $03	31, 31, 0
#00FFFF	$E0, $7F	0, 31, 31

Palette File: snes/palette.a65

512 bytes = 256 colors, 2 bytes each in BGR555.

• Color 0 palette 0 = background (overridden by HDMA gradient)
• Palette 0 = normal text colors
• Palette 1 = bold/highlight text (print_pal = 1)
• Palettes 2-7 = logo and sprite palettes

HDMA Gradient: snes/const.a65 label hdma_pal_src

Format: scanline_count, low_byte, high_byte repeated, $00 terminator.

HDMA channels 1+2 change background color 0 per scanline group:

• Channel 1 writes 0 to CGADD (targets color 0)
• Channel 2 writes BGR555 to CGDATA

Current gradient regions:

• Lines 1-44: Logo area (bright pink)
• Lines 45-54: Black transition
• Lines 55-67: Accent
• Lines 68-178: Graduated dark-to-bright ramp (text area)
• Lines 179+: Bottom border

Designing a new gradient:

1. Choose a base hue
2. Create 10-12 steps from dark to bright
3. Logo area (first ~44 lines) = brightest
4. Ramp dark-to-bright over text area (~110 lines)
5. Bottom border accents

Selection Bar: snes/const.a65 labels hdma_math_src and hdma_bar_color_src

hdma_bar_color_src has two 4-byte entries (normal + highlight):

.byt $RR, $GG, $BB, $GG2  ; normal COLDATA values
.byt $RR, $GG, $BB, $GG2  ; highlight COLDATA values

COLDATA format ($2132): [bit7=B][bit6=G][bit5=R][bits4-0=intensity]

• $3f = R=31, $5f = G=31, $9f = B=31
• $20 = R=0, $40 = G=0, $80 = B=0

Workflow

When the user requests a new color scheme:

1. Convert requested colors to BGR555
2. Generate palette.a65 entries (if modifying text/logo colors)
3. Generate hdma_pal_src gradient table
4. Generate matching hdma_bar_color_src entries
5. Show values with comments
6. After editing, suggest /build then /test to preview